1. Field of the Invention
This invention relates to a punch press and a method of punching plate-type workpieces, and in particular to a punch press provided with one or more than two pairs of discshaped rotatable tool holders each of which supports a plurality of punches or dies, and a method of processing plate-type workpieces by the punch press.
2. Description of the Prior Art
As a conventional punch press is known a turret punch press comprised of a frame, an upper and a lower turrets rotatably mounted on the frame, for carrying a number of punch and die tools at the outer peripheries of the turrets, and a striker attached to the frame, for striking one of the punches. The punch to be struck is positioned or indexed under the striker when the workpiece is punched.
Japanese Patent Publication No. 52-27393 discloses a turret punch press comprised of an upper and lower turrets on which a number of punches and dies are arranged in several concentric circles so that some punches and dies respectively align in the radial directions of the upper and lower turrets. The punch press has a striker movable in a radial direction of the turrets.
U.S. Pat. No. 4,412,469 discloses a turret punch press of which upper and lower turrets carry rotatable punch and die tools. The punch and die tools can be rotated and positioned or indexed as desired.
Another U.S. Pat. No. 4,976,180 discloses a turret punch press provided with upper and lower turrets to which a pair of rotatable disc-shaped tool holders for carrying a plurality of punch and die tools are attached. The position or direction of the tool is changed by the rotation of the tool holder.
In the above-mentioned turret punch press including the upper and lower turrets carrying a number of punch and die tools, the turrets are turned or indexed in order to position the tools with respect to the striker. After the turrets are Indexed as mentioned above, then the tool holder rotates to index the predetermined tools under the striker. The punch and die tools are immovably attached to the holders and are therefore not rotated automatically with respect to the holders. The tools may be rotatably attached to the holders. Making such a complicated configuration, however, in which the tools rotatably mounted on the rotatable holders attached to the rotatable turrets will make the tool portion and the holder portion larger and require larger spaces.